I. Field of the Invention
The invention relates to a proximity switch assembly particularly adapted for use in signaling the location of a movable member.
II. Description of the Prior Art
My prior U.S. Pat. No. 4,664,364 issued on May 12, 1987 discloses a proximity switch assembly for signaling the location of a movable member at either of two opposite end limits of movement relative to a stationary frame. The proximity switch assembly includes a compact, elongate housing adapted to be mounted on the frame to extend along the path of movement of a power-driven member, such as a piston rod, which would shift the movable member between its end limits. A proximity switch is fixedly mounted in the housing and a switch actuating member is mounted for sliding movement over a relatively short distance sufficient to move an actuating tab into and out of actuating proximity to the switch. As the power-driven member approaches one end limit, it slides the switch actuating member within actuating proximity to the switch; and as the power-driven member approaches its opposite end limit, it slides the switch actuating member out of actuating proximity to the switch.
This type of switch assembly is adapted for use in power-actuated clamps of the general type shown in my prior U.S. Pat. No. 4,396,183 issued on Aug. 2, 1983, in which a clamping arm is driven in movement between a closed workpiece clamping position and an open position by the piston rod of a fluid pressure actuated motor. Similar clamps are widely employed in automotive assembly plants to clamp major sheet metal panels, such as roof panels, body side panels and floor panels, in a fixed position while the panels are being welded to each other. In a completely automated system it is essential that all clamps are engaged prior to the welding operation, and the closure of each clamp must be verified by the control system before the robotic welders begin the welding cycle. Similarly, the control system must verify that all clamps are open before the retraction of gates to accommodate the discharge of the welded body from the work station. Substantial operating clearances must be provided in robotic welding systems for movement of several robotic welding heads, which must pass through the clamp carrying gates to reach the seams which are to be welded.
U.S. Pat. No. 4,316,145 discloses a fluid pressure actuator with a proximity position sensor. The proximity position sensor disclosed is a magnetically biased reed switch installed within the cylinder pressure chamber so as to sense the proximity of the piston or a portion of the attached operating rod. Operating circuitry is associated with each proximity switch to provide a delay feature preventing triggering of the associated circuitry upon momentary closing of the reed switch contacts due to mechanical vibrations or other causes. This arrangement requires the cylinder end cap to be modified to provide a mounting for the switch and normally a junction housing must be mounted on the exterior of the cylinder for each proximity switch.
The present invention provides a proximity switch mounted within the cylinder to shield the switch from dirt, weld splatter, etc., which is of extremely compact construction and requires a minimum of structural modification of the fluid pressure actuator.